The invention relates to a device for susceptibility testing of bacterial pathogens and vaccine strains in poultry, in particular chickens, turkeys and ducks.
Two methods are available to the microbiological laboratory for in-vitro susceptibility testing of bacterial pathogens: the diffusion method and the dilution method. The most frequently used diffusion method is the disc agar diffusion method. The resistance test is carried out on a solid medium and the inhibition zone diameter (IZD) is evaluated for a constant concentration of the active substance absorbed in the disc. The inhibition zone diameter breakpoints can be associated with the categories ‘susceptible’, ‘intermediate’ and ‘resistant’.
Also based on the diffusion method, the E-test combines the use of a solid medium with a gradient of the active substance on a paper strip. The formation of an elliptical zone of inhibition allows the minimum inhibitory concentration (MIC) to be determined.
In the dilution method the growth of test bacteria in a liquid medium is tested in the series dilution test in the presence of different concentrations of the active substance. The susceptibility of the pathogen relative to the different concentrations of active substance is analysed by determining the MIC (primary method). For human medicine diagnosis the series dilution test has been established as the standard method of investigation for a high sample throughput. In diagnostic veterinary medicine this is preferably used for bacterial pathogens isolated from pigs and cattle, in order to establish the current resistance situation of bacterial pathogens in livestock. The quantitive method also assists the vet in the choice of active substance and therefore the success of the treatment.
Methods which can be standardised and automated are thus available for susceptibility testing of bacterial pathogens in poultry. There are however no corresponding methods for discriminating and determining field strains and vaccine strains in poultry. Moreover, this is not in combination with an antibiogram.
From this, the object of the invention is to provide a device for susceptibility testing of bacterial pathogens and vaccine strains in poultry which can be standardised and automated.
The device according to the invention for the susceptibility testing of bacterial pathogens and vaccine strains in poultry has a microtiter plate comprising a plurality of wells with at least one well with a coating containing an antibiotic of a marker of a vaccine strain for the vaccination of poultry.
The coating present in at least one well of the microtiter plate allows discrimination between a pathogenic field strain of a bacterial pathogen and the vaccine strain cultivated for vaccination which can be discriminated from the field strain. The discrimination is based on the fact that the vaccine strain comprises a marker which is accompanied by increased resistance or increased susceptibility of the vaccine strain towards an antibiotic. The coating is in the solid state and is applied in a manner known to the person skilled in the art. If a bacterial pure culture in suspension in a suitable nutritive solution is dispensed into a well comprising a coating containing the antibiotic, the antibiotics are thus rehydrated and regain their full effectiveness. After incubation (for example at 35 to 37° C. for 18 to 24 hours) the growth of the bacteria can be measured. Using the growth of the bacteria it can be determined whether it is a pathogen or a vaccine strain. The growth of resistant vaccine strains is not affected by the coating, namely in comparison with field strains. The growth of susceptible vaccine strains, however, is affected by the coating compared to that of field strains. Bacterial growth is indicated by increasing turbidity of the suspension. This can be measured visually or objectively by means of a photometer with no room for interpretation by the user. This allows the uptake of vaccines by poultry to be monitored and field strains to be combatted by a standardised test. The device can also be used for automatic processing.
According to an embodiment at least one well comprises a coating containing an antibiotic of a marker of a salmonella vaccine strain. It refers for example to antibiotics which are markers of salmonella metabolic drift mutants or vaccine strains. Furthermore, it refers, for example, to specific antibiotics which have increased susceptibility to the salmonella vaccine strain due to an envelope marker. Similar salmonella vaccine strains are revealed in the European Patent EP 0 263 528 B1 (in particular in the claims and in the tables in lines 26 to 49 of page 5) and in the European Patent EP 0 642 796 B1 (in particular in the claims and the tables on page 6, lines 30 to 46). The publication of the two European Patents relating to salmonella metabolic drift mutants and salmonella envelope mutants is included in the present Application. Corresponding live marker vaccines for poultry are marketed by the Applicant under the trademark Salmonella VAC® T and Salmonella VAC® E.
According to an embodiment of the invention at least one well has a coating containing an antibiotic selected from the antibiotics Streptomycin (STRE), Rifampicin (RAM), Erythromycin (ERYD). Streptomycin and Rifampicin are metabolic drift markers of vaccine strains which are cited in EP 0 263 528 B1 and EP 0 642 796 B1. The vaccine strains cited in EP 0 642 796 B1 have an envelope marker which gives it an increased susceptibility relative to Erythromycin. Salmonella VAC® T and VAC® E have been developed on the basis of vaccine strains from the two Patents.
According to an embodiment at least one well contains a coating comprising a therapeutically relevant antibiotic for poultry. This makes it possible to check the effectiveness of a therapeutically relevant antibiotic for poultry against a bacterial culture isolated from poultry. In this test an isolated bacterial culture in suspension in a suitable nutritive solution is also dispensed into the well and incubated. Finally, the growth of the bacterial culture is verified with reference to the turbidity. Changes in the susceptibility and the resistance of bacterial isolates towards antibiotics are visible therefrom. This information can be used for determining the state of health of poultry, monitoring resistance and for therapeutic treatment by the vet.
The coating contains an antibiotic which is a therapeutically relevant antibiotic and which is of particular significance or frequently used for the treatment of infectious diseases of poultry. Preferably a plurality of wells with different coatings are provided with a plurality of therapeutically relevant antibiotics. The therapeutic relevance of antibiotics can change over time. New therapeutically relevant antibiotics can appear. The invention includes all antibiotics which at the time and in the future are important for the therapeutic treatment of poultry.
One embodiment comprises at least one well with a coating comprising an antibiotic selected from the antibiotics Ampicillin (AMP), Ceftiofur (CET), Colistin (CST), Enrofloxacin (ENRO), Erythromycin (ERY), Gentamicin (GEN), Lincomycin (LIN), Neomycin (NEO), Oxacillin (OXA), Penicillin G (PEN), Spectinomycin (SPEC), Streptomycin (STRE), Tetracycline (TET), Tiamulin (TIA), Trimethoprim-sulfamethoxazole (T/S). It also refers to antibiotics which have been determined by the Applicant to be currently of high therapeutic relevance for poultry. Ceftiofur is not allowed for the treatment of poultry. Determining the use of Ceftiofur is however interesting for the diagnosis. A plate with a plurality of wells with coatings comprising different antibiotics allows an antibiogram to be established for a bacterial culture isolated from poultry.
If the antibiotic has a predetermined concentration in the coating, a quantitive report on the effectiveness of the antibiotic against the pathogen or the vaccine strain is possible. The test is preferably carried out in accordance with the documentation of the standard procedure criteria, which have been issued by the National Committee for Clinical Laboratory Standards (NCCLS), Wayne, Pa., USA. These are to be found in: National Committee for Clinical Laboratory Standards (2002); Performance Standards for Antimicrobial Disk and Dilution Susceptibility Tests for Bacteria Isolated from Animals; Approved Standard—Second Edition, Document M31-A2, Vol. 22, No. 6, NCCLS, Wayne, Pa., USA.
According to a further embodiment, the coatings of different receivers contain the same antibiotics in different concentrations. This allows quantitive information taken on the MIC as to the effectiveness of an antibiotic against a bacterial culture isolated from poultry. The effectiveness of the antibiotic in-vitro against a specific pathogen can be determined using MIC breakpoints. These are shown corresponding to the clinical categories as susceptible, intermediate and resistant.
Moreover, according to an embodiment, coatings of different receivers contain the antibiotic in a concentration corresponding to the lower breakpoint and the upper breakpoint. The lower breakpoint corresponds to an MIC value which completely prevents sufficient and visible bacterial growth, ie the bacterial isolate is susceptible to the antibiotic. The upper breakpoint corresponds to an MIC value which only partially prevents sufficient and visible bacterial growth and indicates intermediate effectiveness of the antibiotic. Therefore the measurement of MIC values over the upper breakpoint indicates the resistance of the bacterial isolate toward a specific antibiotic. The lower breakpoint and upper breakpoints are respectively taken from the current documentation.
For the embodiment of the invention references are provided in the section of the description devoted to carrying out the test. The wells are coated with the active substance or the antibiotic, such that the desired concentration of active substance is reached by introducing a defined sample amount in the sample.
According to a further embodiment a plurality of wells have the same coating. This allows comparative measurements which increase the reliability of the susceptibility test.
One embodiment comprises at least one well without a coating. This allows a comparative measurement on a bacterial culture, of which the growth is not affected.
One embodiment comprises a plurality of groups of wells, the wells in the groups comprising different coatings and the wells of different groups the same coatings. As a result further comparative measurements are possible.
According to a further embodiment the microtiter plate has 96 wells. This format facilitates working with manual pipettes, in particular. The invention however relates to microtiter plates with a different number of wells, for example 384 or 1536 wells which are in particular suited for processing by robots.
According to an embodiment the microtiter plate is packed in an airtight pouch and as a result the effectiveness of the coatings is guaranteed over a lengthy storage time at room temperature (15-25° C.). According to a further embodiment the pouch also contains a dessicant.